The present disclosure relates to a reactor assembly for processing substrates and more particularly, to a distribution system for flowing gases and/or reactants into and out of the reactor assembly process and apparatus for treating a substrate and, more particularly, to a dielectric barrier discharge apparatus and processes for treating a surface of the substrate.
Plasmas and plasma generation have been studied for many years. There are several types of plasma generators currently employed for numerous applications. A large majority of these plasma generators require vacuum systems that operate at about 1 to about 10 torr and employ sophisticated, expensive plasma sources such as microwave plasma generators as used in many downstream plasma ashers, radio frequency(rf) plasma generators, combinations comprising at least one of the foregoing plasma sources, and the like.
Other types of plasma generators are designed to operate at atmospheric pressures, which avoid the use, complexity, and cost of the aforementioned vacuum and plasma systems. However, atmospheric plasma tools are generally limited in spatial extent(on the order of a few centimeters) requiring various techniques such as wafer rotation or scanning of the plasma source to overcome this limitation and provide uniform ashing.
In atmospheric plasma tools, the plasma is typically generated from arcs across spaced apart electrodes. For example, in U.S. Pat. No. 5,414,324 for xe2x80x9cOne Atmosphere, Uniform Glow Discharge Plasma,xe2x80x9d a one-atmosphere, steady-state glow discharge plasma generated between a pair of insulated, equally spaced planar metal electrodes energized with an rms potential of 1 to 5 kV at 1 to 100 kHz is described. The patentees state that glow discharge plasmas are produced by free electrons, which are energized by imposed direct current or rf electric fields. These electrons collide with neutral molecules transferring energy thereto, thereby forming a variety of active species that may include metastables, atomic species, free radicals, molecular fragments, monomers, electrons, and ions. An environmental isolation enclosure in which a low feed gas flow is maintained surrounds the plate assembly in order to equal the leakage rate of the enclosure. In fact, a no flow condition is taught for normal operation of the apparatus. Materials are processed by passing them through the plasma between the electrodes, where they are exposed to all plasma constituents including ions. The use of bare electrodes inevitably introduces particles that can deleteriously compromise the integrity of the circuits produced on the wafers. Additionally, the electrical currents (DC or AC) may damage the devices being manufactured on the substrate, e.g., wafer, causing lower yields.
Another type of atmospheric plasma discharge apparatus includes dielectric discharge barrier apparatuses. The dielectric barrier discharge apparatus generally includes two parallel electrodes with a dielectric-insulating layer disposed on or between one of the electrodes and operate at about atmospheric pressures. The dielectric barrier discharge apparatus does not provide one single plasma discharge, but instead provides a series of short-lived, self terminating arcs, which on a long time scale (greater than a microsecond), appears as a stable, continuous, and homogeneous plasma. The dielectric layer serves to ensure termination of the arc. The wafer to be treated is often used as one of the planar electrodes or typically is placed between two planar electrodes. In either scenario, the discharges generated by the dielectric discharge barrier apparatus pass through the wafer, thereby damaging the circuitry previously formed in the wafer or causing localized variations in the ashing rate.
In U.S. Pat. Nos. 5,198,724 and 5,369,336, the patentees describe an apparatus that includes a central electrode, a peripheral cylindrical electrode surrounding the central conductor, and an insulating cylinder interposed between the electrodes in order to prevent direct arc discharge from occurring therebetween. The electrodes and the insulating cylinder are coaxially arranged in order to define a cylindrical discharging space therein. By applying high-frequency electrical energy to the central electrode, a glow discharge is caused to occur between the central electrode and the insulating cylinder. A reactive gas is introduced from one end of the discharge space, excited by the glow discharge and exits from the other end as excited plasma impinging on a work piece to be processed by the plasma. However, the apparatus cannot be scaled to large dimensions since the insulating cylinder must remain thin because it is required to conduct the radio frequency discharge current. Further, the dielectric material is subject to attack by the reactive gases, and introduces a phase lag, which requires that higher voltages and lower currents must be employed to maintain the discharge.
Another problem with this type of atmospheric plasma discharge apparatus is specific to the manufacture of semiconductor devices. Providing even distribution of the reactants onto the surface of the semiconductor substrate is desired. Because the discharge tubes of these create reactants, which move radially in all directions, they do not provide, even application of reactants in a particular desired direction. This is because the reactants concentration is altered by its passing through the elements of the device, such as quartz tubes, electrodes, and by being absorbed by the emitter gas itself. The reactants not reaching the wafer are therefore wasted. Additionally, the geometry of cylindrical emitters with a central electrode surrounded by the other electrode inherently produces uneven reactants. Uneven distribution of reactants results in uneven exposure to the flat wafer, thereby resulting in uneven treatment of the surface, thereby reducing the precision and consistency of the exposure of a semiconductor wafer to the reactants.
Attempts in the prior art to overcome uneven distribution include apparatuses wherein the semiconductor substrate is used as one of the planar electrodes or resides between planar electrodes. However, these types of prior art devices suffer from the same problem of localized loss of dielectric efficacy and uneven plasma generation. Additionally, with many of the prior art devices, there is no means for cooling the electrodes, and further degradation of the dielectric material and heating of the gas results in inefficiency and short useful device lifetime.
In those dielectric discharge barrier apparatuses that employ a screen electrode or grid, the screen electrode or grid typically comprises a woven metal lattice pattern. The problem with these types of screen electrodes is that the overlapping wires of the woven pattern provide only a few arc sites. The areas of overlap closest to the dielectric layer provide arc sites whereas the areas of overlap farthest from the dielectric layer generally do not arc at the voltages employed, greatly reducing the efficiency of the plasma as a source for reactants.
Disclosed herein are a dielectric discharge apparatus and process for treating a substrate. The dielectric barrier discharge apparatus comprises a first planar electrode; a dielectric layer disposed on a surface of the first planar electrode; a second planar electrode spaced above in a parallel plane with the dielectric layer, wherein the second planar electrode comprises a porous structure having a nominal thickness and a geometric transmission factor greater than about 70 percent; and a power supply in electrical communication with the first electrode and the second electrode.
In another embodiment, the apparatus comprises a first planar electrode; a dielectric layer disposed on a surface of the first planar electrode; a second planar electrode spaced above and in a parallel plane with the dielectric layer, wherein the second planar electrode comprises a porous structure; a substrate spaced above in a parallel plane with the second planar electrode and at a distance less than or equal to about 10 millimeters from the second planar electrode; and a power supply in electrical communication with the first electrode and the second electrode.
A process for treating a substrate comprises introducing a substrate to be treated into a chamber, wherein the. chamber comprises a dielectric barrier discharge apparatus comprising a first planar electrode, a dielectric layer disposed on the first planar electrode, a second planar electrode spaced above and in a parallel plane with the dielectric layer, and a power supply in electrical communication with the first and second planar electrodes, wherein the second planar electrode is porous and has a geometric transmission factor greater than about 70 percent, and wherein introducing the substrate comprises positioning the substrate above the second planar electrode in a parallel plane and at a distance less than or equal to about 10 millimeters from the second planar electrode; flowing an oxygen containing fluid between the first and second electrodes at about an atmospheric pressure; pulsing the power supply to the electrodes and generating a plasma comprising reactive species between the first planar electrode and the second planar electrode; and reacting the reactive species with the substrate.
The above described and other features are exemplified by the following figures and detailed description.